Abstract: Streptococcus mutans-induced caries formation continues to be a major problem in developed and developing nations which, according to the World Health Organization, impacts 60-90% of children world-wide (123). Despite widespread water fluoridation and the implementation of educational programs aimed at improving oral health in the United States, recent reports reveal no significant improvement in the prevalence or severity of dental caries in the primary dentition (62, 115). Moreover, approximately 90% of adult Americans have dental caries in their permanent teeth, contributing to the nation's estimated costs for dental treatment that exceeded $70 billion in 2002 (42). Since the survival and virulence of S. mutans is directly related to the availability and transport of essential metal ions in the plaque environment, particularly iron and manganese, metal ion uptake mechanisms represent attractive targets for drug design aimed at combating cavities. In the present grant application, we profess a novel approach to alleviating tooth decay that is centered on investigating global virulence gene regulation by the S. mutans SloR metalloregulatory protein. During the previous grant term, we confirmed SloR-dependent repression of S. mutans metal ion transport genes and virulence factors when sustainable levels of manganese are achieved (such as during a mealtime), and loss of this repression when metal ions become limiting (such as between meals). These observations led us to hypothesize that enhanced SloR repression at physiological manganese concentrations will attenuate S. mutans virulence gene expression and impede the process of cariogenesis. This application sets out to address this hypothesis by elucidating the structural basis for SloR activation and DNA binding in S. mutans using molecular and biochemical approaches. Crystallographic analysis of the wild-type and mutant SloR protein coupled with DNA footprinting and DNA bending experiments will elucidate the details of the SloR:DNA interaction and reveal potential mechanisms of metalloregulation so that ultimately new therapeutic agents that target SloR activity can be designed.